KR102774781B1 - Electrolyte additive for manufacturing metal electrode - Google Patents

Abstract

The present invention provides an electrolyte additive for manufacturing a metal electrode, an electrolyte containing the same, a metal electrode manufactured using the same, and a method for manufacturing a metal electrode using the same. When an electrolyte containing the electrolyte additive of the present invention is used, electrodeposited lithium may have a large and round shape, which may be advantageous in suppressing dendrite formation, and electrodeposition overvoltage may be reduced due to improved lithium ion reactivity. In addition, when an electrolyte containing the electrolyte additive of the present invention is used, the lifespan of the electrode may be improved, and the mechanical strength and flexibility of the electrodeposited surface may be improved.

Description

Electrolyte additive for manufacturing metal electrode {Electrolyte additive for manufacturing metal electrode}

The present invention relates to an electrolyte additive for manufacturing a metal electrode.

Lithium is not only the lightest metal, but also has a low reduction potential and a large theoretical capacity, so it is being studied as a next-generation cathode material. In the case of lithium secondary batteries using lithium metal as an electrode, a thin lithium electrode is required to maximize the efficiency and energy density of the battery, but the existing physical rolling method for manufacturing lithium foil has limitations in manufacturing lithium foil with a thickness below a certain level.

Accordingly, lithium electrodes are being manufactured by applying the electroplating method to overcome the limitations of implementing the thin film thickness of the rolling method. At this time, since the composition of the electrolyte used in the electroplating can affect the shape of the electrodeposited lithium and the lithium surface SEI layer, research on electrolyte additives for improving the performance of the lithium electrodeposited electrode is necessary.

Specifically, research is needed on electrolyte additives for manufacturing metal electrodes and electrolytes containing the same that can improve the performance of batteries by inducing lithium deposition in a shape advantageous for lithium dendrite suppression and forming an SEI film that is effective in accommodating volume changes due to lithium insertion/deinsertion.

1. Im Rana, Lee Min-hee, and Kim Jeom-soo, Characteristics of lithium electrodes fabricated under various deposition conditions. Journal of the Korean Electrochemical Society, Vol. 22, No. 3, 2019, 128-137.

The present invention aims to provide an electrolyte additive for inducing a surface film that is effective in improving the performance of a metal battery. Specifically, the present invention aims to provide an electrolyte additive for lithium electrodeposition for inducing a surface film that is effective in improving the performance of a lithium metal battery.

The present invention provides an electrolyte for manufacturing a metal electrode.

At this time, as an embodiment, an electrolyte additive for manufacturing a metal electrode is provided, wherein the electrolyte contains at least one material selected from the group consisting of FEC (Fluoroethylene carbonate) and LiDFOB (Lithium Difluoro Oxalato Borate).

In one embodiment, the metal provides an electrolyte additive for manufacturing a metal electrode, wherein the metal is lithium.

In addition, the present invention provides an electrolyte for manufacturing a metal electrode, comprising the additive.

In one embodiment, the metal is lithium, and an electrolyte for manufacturing a metal electrode is provided.

In one embodiment, the electrolyte for manufacturing a metal electrode is provided, wherein the electrolyte contains 0.25 to 0.37 M of the LiDFOB.

In one embodiment, the electrolyte for manufacturing a metal electrode is provided, wherein the electrolyte contains 0.20 to 0.30 M of the FEC.

In addition, the present invention provides a metal electrode manufactured using the above electrolyte.

In one embodiment, the metal provides a metal electrode, wherein the metal is lithium.

In one embodiment, a metal electrode is provided, wherein the film of the electrode includes one or more components selected from the group consisting of LiF, BO, BF ₂ , and BF .

In one embodiment, a metal electrode is provided, wherein the film of the electrode has a value of LiF:Li _x PF _y among the Li components of 80:20 to 90:10 (element %).

In one embodiment, a metal electrode is provided, wherein the film of the electrode has a B-O bond ratio value of 70 to 90 element % among the B components.

In one embodiment, a metal electrode is provided, wherein the film of the electrode contains B elements and F elements in a ratio of 1:3 to 1:5.

In addition, the present invention provides a method for manufacturing a metal electrode using the above electrolyte.

In one embodiment, a method is provided wherein the metal is lithium.

In one embodiment, the method provides a method for manufacturing a metal electrode having a high stripping efficiency compared to using an electrolyte that does not include the additive.

In one embodiment, the method provides a method that increases the rounded shape of the deposited lithium shape compared to using an electrolyte that does not include the additive.

In one embodiment, the method provides a method for manufacturing a metal electrode in which the formation of dendrites is reduced compared to using an electrolyte that does not include the additive.

When using an electrolyte containing the electrolyte additive of the present invention, the electrodeposited lithium may have a large and round shape, which may be advantageous in suppressing dendrite formation.

When using an electrolyte containing the electrolyte additive of the present invention, the electrodeposition overvoltage can be reduced due to improved lithium ion reactivity.

When an electrolyte solution containing the electrolyte additive of the present invention is used, the life maintenance rate of the electrode can be improved.

When an electrolyte solution containing the electrolyte additive of the present invention is used, the mechanical strength and flexibility of the electrodeposited electrode surface can be improved.

Figure 1 shows the results of comparing the electrodeposited lithium morphology according to the presence and type of electrolyte additive.
Figure 2 shows the results of comparing the initial overvoltage and stripping efficiency according to the presence and type of electrolyte additive.
Figures 3 to 4 show the results of half-cell tests compared with and without electrolyte additives.
Figures 5 to 6 show the results of comparing the composition of the electrodeposited lithium surface film according to the presence or absence of electrolyte additives and the composition ratio.
Figures 7 and 8 show the results of a full cell test comparing lithium negative electrodes electrodeposited using commercial lithium foil and electrolyte with electrolyte additives.

All technical and scientific terms used herein, unless otherwise defined, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

Ⅰ. Electrolyte additives

The present invention provides an electrolyte additive. For example, the electrolyte additive may be an electrolyte additive for manufacturing a metal electrode. For a specific example, the electrolyte additive may be an electrolyte additive for manufacturing a lithium electrode. The lithium electrode manufacturing may refer to the manufacturing of a lithium electrode by an electroplating method used to overcome the limitations of implementing a thin film thickness that a rolling technology has.

At this time, the additive may include at least one material selected from the group consisting of, for example, FEC (Fluoroethylene carbonate), LiBOB (Lithium Bis(Oxalate) Borate), LiFSI (Lithium bis(fluorosulfonyl)imide), and LiDFOB (Lithium Difluoro Oxalato Borate). As a specific example, the additive may include at least one material selected from the group consisting of FEC (Fluoroethylene carbonate) and LiDFOB (Lithium Difluoro Oxalato Borate). The additive may affect lithium electrodeposition, and thus may help lithium to be electrodeposited in a shape advantageous for suppressing the formation of lithium dendrites. In addition, it may help improve the performance of the battery by forming a surface film that is effective in accommodating volume changes due to lithium insertion/desorption.

Ⅱ. Electrolyte

The present invention provides Ⅰ. An electrolyte comprising an electrolyte additive. For example, the electrolyte may be an electrolyte for manufacturing a metal electrode, and as a specific example, it may be an electrolyte for manufacturing a lithium electrode.

The above electrolyte may include, for example, one or more substances selected from the group consisting of EC (ethylene carbonate), DMC (dimethyl carbonate), DEC (diethyl carbonate), and EMC (ethyl methyl carbonate), LiPF ₆ , and the above I. electrolyte additive.

At this time, as an example, the electrolyte may contain LiDFOB at 0.05 to 0.70 M. As a specific example, the electrolyte may contain LiDFOB at 0.25 to 0.50 M, and when LiDFOB in the above range is added, it may be most preferable in that it has high stripping efficiency. In addition, as an example, the electrolyte may contain FEC at 0.20 to 0.30 M. In addition, as an example, the electrolyte may contain LiDFOB at 0.25 to 0.50 M and FEC at 0.20 to 0.30 M.

As a specific example, the electrolyte may be a mixture of 1 M LiPF ₆ in EC/DMC and additives including 0.37 M LiDFOB and 0.25 M FEC.

Ⅲ. Electrode

The present invention provides a metal electrode manufactured using Ⅱ. an electrolyte. For example, the metal may be lithium. At this time, the lithium electrode manufactured using the electrolyte may be characterized in that lithium having a round shape advantageous for suppressing the growth of lithium dendrites is deposited, and a surface film effective for accommodating volume changes due to lithium insertion/desorption is formed.

At this time, the film of the electrode may include, as an example, one or more components selected from the group consisting of LiF, BO, BF ₂ , and BF .

In addition, the film of the electrode may have, as an example, a value of LiF:Li _x PF _y among the Li components of 60:40 to 95:5 (in element %). As a preferred example, a value of LiF:Li _x PF _y among the Li components of 80:20 to 90:10 (in element %).

In addition, the film of the electrode may have, as an example, a ratio value of B-O bonds among the B components of 50 to 99 element %. As a preferred example, the film of the electrode may have, as an example, a ratio value of B-O bonds among the B components of 70 to 90 element %.

In addition, the film of the electrode may, as an example, contain B elements and F elements in a ratio of 1:1 to 1:7 (element %). In a preferred example, contain B elements and F elements in a ratio of 1:3 to 1:5.

At this time, the above components and composition ratio may be essential conditions in terms of mechanical strength and flexibility of the electrode surface.

Ⅳ. Manufacturing method

The present invention provides Ⅱ. a method for manufacturing a metal electrode using an electrolyte. In one embodiment, the metal may be lithium.

At this time, the method may be Ⅰ. a method for manufacturing a metal electrode having a high stripping efficiency compared to using an electrolyte that does not include an electrolyte additive. In addition, the method may be Ⅰ. a method for increasing a round shape of a deposited lithium shape compared to using an electrolyte that does not include an electrolyte additive. In addition, the method may be Ⅰ. a method for manufacturing a metal electrode in which the formation of dendrites is reduced compared to using an electrolyte that does not include an electrolyte additive. In addition, the method may be Ⅰ. a method for reducing lithium deposition overvoltage by improving the reactivity of lithium ions compared to using an electrolyte that does not include an electrolyte additive.

That is, when a metal electrode is manufactured using an electrolyte containing the above I. electrolyte additive, lithium is deposited in a round shape that is advantageous for suppressing dendrite formation, and a metal electrode having high lithium stripping efficiency and a film having excellent mechanical strength and flexibility can be manufactured, which can affect the improvement of the efficiency and life performance of the electrode.

V. Battery

The present invention provides a secondary battery including a metal electrode manufactured using the above II. electrolyte. The secondary battery refers to a battery that can be recharged and used repeatedly even after discharge, and more specifically, it may refer to a battery including a positive electrode, a negative electrode, a separator, and an electrolyte. The shapes and compositions of the positive electrode, the negative electrode, the separator, and the electrolyte include all those known in the art.

The secondary battery may be a secondary battery including lithium, zinc, aluminum, magnesium, iron, calcium, sodium, etc., and as a preferred embodiment, may be a lithium battery including a lithium ion battery and a lithium-sulfur battery. At this time, the secondary battery has no particular limitation on the shape of the battery, and may include all of a cylindrical shape, a coin shape, a pouch shape, etc.

In the case of the secondary battery provided in the present invention, the formation of dendrites is suppressed and it can have an increased cycle life. Accordingly, the secondary battery can be applied to devices requiring high-output, long-life secondary batteries, including electric vehicles, hybrid electric vehicles, and electric two-wheeled vehicles.

Hereinafter, the present invention will be described in more detail through examples. It will be apparent to those skilled in the art that these examples are intended only to illustrate the present invention, and the scope of the present invention is not to be construed as being limited by these examples.

Example 1. Electrolyte design

A electrodeposition electrolyte was prepared by applying various types of additives to the ester-based electrolyte of a conventional lithium ion battery system.

Among FEC(Fluoroethylene carbonate), LiDFOB(Lithium Difluoro Oxalato Borate), LiBOB(Lithium Bis(Oxalate) Borate), and LiFSI(Lithium bis(fluorosulfonyl)imide), one material was applied alone, and the material with the best effect was selected based on the shape of the electrodeposited lithium and the ICE evaluation results. According to Fig. 1, LiDFOB and FEC had the best effects, so they were selected as the two materials. The two materials were prepared at various mixing ratios as shown in Table 1, and then applied as electrolyte additives to compare and analyze the lithium electrode characteristics. At this time, 1M LiPF ₆ in EC/DMC (3:7 vol%) was used as the base electrolyte, and the additives of each composition in Table 1 were added to conduct the experiment.

LiDFOB[M(mol/L)] FEC[M(mol/L)] 1 0.12 LiDFOB 0.25 FEC 2 0.25 LiDFOB 3 0.37 LiDFOB 4 0.50 LiDFOB

Experiments using an electrolyte containing the above electrolyte additive were performed under the following conditions.

Lithium plating

Current density: 0.4 mA cm ^-2 (4 mAh cm ^-2 )

Electrolyte additives

FEC (Fluoroethylene carbonate)

LiDFOB (Lithium Difluoro Oxalato Borate)

Lithium plating electrolyte

Base electrolyte: 1M LiPF ₆ in EC/DMC (3:7 vol%)

Additive included: 1M LiPF ₆ in EC/DMC (3:7 vol%) + [0.37M LiDFOB + 0.25M FEC]

Lithium Stripping

Current density: 0.2 mA cm ^-2 (4 mAh cm ^-2 )

Termination: 1.0 V cut-off

Electrolyte: 1M LiPF ₆ in EC/DEC/DMC (1:2:1 vol%) + 2 wt% VC

Example 2. Comparison of electrodeposited lithium shapes

Plating conditions: 4 mA cm ^-2 @ 4 mAh cm ^-2 (7.069 mAh) and SEM analysis conditions: 5 kV were used to compare the morphology of electrodeposited lithium. A thin-film lithium electrode was manufactured by electrodepositing lithium in an amount of 4 mAh cm ^-2 on a current collector (Cu foil) by the electroplating method. When the basic electrolyte (1 M LiPF ₆ in EC/DMC) was applied, lithium with an uneven particle size and shape of long needles was electrodeposited, and when LiDFOB and FEC were applied as a single additive, the lithium particles were formed in a relatively round shape. When the composite additive was applied, it was confirmed that there was an effect of having large and round lithium particles compared to the basic electrolyte. That is, the height-to-base ratio of the lithium particles decreased (see Fig. 2).

Example 3. Comparison of deposition overvoltage

The deposition overvoltages were compared under plating conditions: 4 mA cm ^-2 @ 4 mAh cm ^-2 (7.069 mAh) and stripping electrolyte: 1 M LiPF ₆ in EC/DEC/DMC (1:2:1 vol%) + 2 wt% VC. When the [LiDFOB+FEC] combination additive was applied, the deposition overvoltage was confirmed to decrease (initial IR: -0.11 V → -0.09 V, deposition overvoltage: -0.04 V → -0.02 V). When 1 M LiPF ₆ in EC/DMC + [0.37 M LiDFOB + 0.25 M FEC] was applied, the highest efficiency of 94.4% was confirmed. As a result of the efficiency evaluation, the optimal additive ratio was [0.37 M LiDFOB + 0.25 M FEC] (see Fig. 3).

Example 4. Lifespan comparison

Li/Cu half-cell cycle test was conducted under the conditions of electrode utilization: 25% (4 mAh cm ^-2 @ 1 mAh cm ^-2 ), cycle test electrolyte: 1 M LiPF ₆ in EC/EMC/DMC (3:4:3 vol%) + 5 wt% FEC, pre-cycle 0.1 mA cm ^-2 @ 1 mAh cm ^-2 (0.1C-rate), 0.5 mA cm ^-2 @ 1 mAh cm ^-2 (0.5C-rate). The life evaluation of the electrode manufactured by applying [0.37 M LiDFOB + 0.25 M FEC] as the electrodeposition electrolyte and commercial 20 ㎛ Li foil was performed (Li/Cu half cell). It was confirmed that [0.37M LiDFOB+0.25M FEC] showed the best life maintenance rate based on 20 cycles (20㎛ Li: 91.0% vs. 0.37M+0.25M: 95.6%). It was confirmed to show better life characteristics than the 20㎛ commercial Li foil with the same utilization rate (1 mAh cm ^-2 @ 4 mAh cm ^-2 ; 25%) (see Fig. 4).

Example 5. Comparison of Electrodeposited Lithium Surface Film Compositions

The experiment was conducted under plating conditions: 4 mA cm ^-2 @ 4 mAh cm ^-2 (7.069 mAh) and XPS analysis conditions: 12 kV, 72 W, monochromated Al Ka, hv = 1486.6 eV. The results of the analysis of the surface film components of the electrodeposited lithium electrode showed that the products resulting from the decomposition of the organic solvent when the basic electrolyte was applied became the main component of the film. In addition, it was confirmed that the mechanical strength and flexibility of the electrode surface electrodeposited with the designed electrolyte were improved, and it was confirmed that the film at this time necessarily contained LiF, BO, BF ₂ , and BF components. Specifically, the ratio of LiF should be greater than Li _x PF _y , and it was confirmed that the ratio at this time was maintained as LiF : Li _x PF _y = 80-90 : 20-10 (element %). In addition, it was confirmed that BF and BO exist through the decomposition of LiDFOB, and at this time, the BO bond accounts for about 80% of the element (see Fig. 5).

In addition, it was confirmed that the overall element ratio of the lithium surface film formed with the designed electrolyte was composed of 3.4 element % of the B element and 12.9 element % of the F element. It was confirmed that when the B element and the F element exist in a ratio of 20:80, it is advantageous for the formation of a film having excellent mechanical strength and flexible properties that are the cause of improved initial efficiency and life performance of the lithium electrode (see Fig. 6).

Example 6. Full cell test

Full cell test was performed under the following conditions: Li Plating Condition: 4 mA cm ^-2 @ 4 mAh cm ^-2 (7.069 mAh), Cycle test Electrolyte: 1M LiPF ₆ in EC/EMC/DMC(3:4:3 vol%) + 5 wt% FEC, Voltage range: 2.5 - 4.5 V, Loading(PE): 11.5 mg cm ^-3 , Electrode density(PE): 2.8~2.9 g cm ^-3 , Capacity(PE): 180 mAh g ^-1 .

LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (NCM622) was applied as the anode, and the lithium electrodeposited with the electrolyte with the additives and the full cell evaluation were performed. In the formation evaluation, it was confirmed that the lithium electrodeposited with the electrolyte with the additives, when used as the anode, showed the same level of initial efficiency as that of commercial Li foil (89.7% vs. 89.8% at 0.1C) (see Fig. 7). In addition, the result of the 1C/1C life evaluation showed the efficiency and capacity retention rate similar to those of commercial lithium at 20 cycles (97.9% vs. 99.1%). By applying 1 M LiPF ₆ in EC/DMC + [0.37 M LiDFOB + 0.25 M FEC] as the electrodeposition electrolyte, it was confirmed that the improved morphology of the electrodeposited lithium and the enhanced initial efficiency of the electrode can have a positive effect on maintaining cycle stability and Coulombic efficiency (see Fig. 8). That is, through Li/Cu half and Li/NCM622 full cell life characteristic experiments, it was confirmed that a similar level of performance as commercial lithium foil can be achieved even with an electrodeposited lithium electrode.

Claims (17)

An electrolyte additive for lithium electrode manufacturing, comprising FEC (Fluoroethylene carbonate) and LiDFOB (Lithium Difluoro Oxalato Borate).
delete An electrolyte for manufacturing a lithium electrode, comprising the additive of claim 1.
delete In the third paragraph,
An electrolyte for manufacturing a lithium electrode, wherein the electrolyte contains 0.25 to 0.50 M of the LiDFOB.
In the third paragraph,
An electrolyte for manufacturing a lithium electrode, wherein the electrolyte contains 0.20 to 0.30 M of the FEC.
A lithium electrode manufactured using the electrolyte of claim 3.
delete In Article 7,
A lithium electrode, wherein the film of the electrode comprises one or more components selected from the group consisting of LiF, BO, BF ₂ , and BF .
In Article 7,
A lithium electrode, wherein the film of the electrode has a value of LiF:Li _x PF _y among the Li components of 80:20 to 90:10 (element %).
In Article 7,
A lithium electrode, wherein the film of the electrode has a ratio value of 70 to 90% of the BO bond among the B components.
In Article 7,
A lithium electrode, wherein the film of the electrode contains B elements and F elements in a ratio of 1:3 to 1:5.
A method for manufacturing a lithium electrode using the electrolyte of claim 3.
delete In Article 13,
The above method is a method for manufacturing a lithium electrode having a high stripping efficiency compared to using an electrolyte solution that does not include the additive of claim 1.
In Article 13,
The method is a method for increasing the round shape of the deposited lithium shape compared to using an electrolyte solution that does not include the additive of claim 1.
In Article 13,
The method is a method for manufacturing a lithium electrode in which the formation of dendrites is reduced compared to using an electrolyte that does not include the additive of claim 1.